25.py

# Returns index of x in arr if present, else -1
def binarySearch (arr, l, r, x):
 
    # Check base case
    if r >= l:
 
        mid = int(l + (r - l)/2)
 
        # If element is present at the middle itself
        if arr[mid] == x:
            return mid
         
        # If element is smaller than mid, then it 
        # can only be present in left subarray
        elif arr[mid] > x:
            return binarySearch(arr, l, mid-1, x)
 
        # Else the element can only be present 
        # in right subarray
        else:
            return binarySearch(arr, mid+1, r, x)
 
    else:
        # Element is not present in the array
        return -1
 
# Test array
arr = [ 2, 3, 4, 10, 40 ]
x = 40
 
# Function call
result = binarySearch(arr, 0, len(arr)-1, x)
 
if result != -1:
    print("Element is present at index {}".format(result))
else:
    print("Element is not present in array")